JPH0253937B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a dielectric material with a perovskite-type structure starting from an alkaline earth zirconate in which 10 mol % of zirconium is replaced by titanium. Dielectric materials of this type are important in the manufacture of capacitors, especially multilayer capacitors. Monolithic ceramic multilayer capacitors can combine a high degree of reliability with a very high capacitance in a small volume. The ceramic starting material is combined into a thin film with a binder. A metal paste forming an electrode is then applied to the ceramic film, and the films are then stacked. For this purpose, ceramic films and metal paste are stacked alternately. In order to sinter the structure formed from the layer of dielectric material and the electrodes together, the material of the electrodes and the sintering conditions need to be chosen such that the metal layer does not melt and is not oxidized. It is known to produce multilayer capacitors by densely sintering ceramic materials in air at temperatures above 1300°C. At this sintering temperature,
Noble metals with high melting points such as palladium or platinum are suitable as electrode materials. Two types of ceramic materials used as dielectrics for capacitors can be distinguished, giving rise to different types of end products: 1. In the first type, the maximum possible capacitance per unit of volume is (Type 2 capacitor), which uses a material made of ferroelectric material with an extremely high dielectric constant as the dielectric. Ferroelectric ceramic materials can be understood as meaning compounds with a BaTiO ₃ content of 70 mol % or more. 2 The second type requires the minimum possible loss of the capacitor and stable characteristics against temperature changes and electric field strength changes (amplitude, frequency) (Type 1 - capacitor). The present invention relates to a second type of ceramic material, in which the quality of ferromagnetic ceramic materials is unsatisfactory for use in multilayer capacitors with high stability and high dielectric properties. In order to be able to produce inexpensive multilayer capacitors, the use of palladium-silver alloy electrodes instead of palladium electrodes in a second type of capacitor is described in US Pat. No. 3,811,937. However, given the required minimum palladium content of 30% by weight in the electrode material, such multilayer capacitors are relatively expensive components. For completeness of explanation, the dielectric consisting of alkaline earth zirconate substituted with titanium is RC
Kell et al., J. Am. Cer. Soc. 56 (1963), No. 7, page 53, but these dielectrics must be sintered in air at temperatures of at least 1500°C. For this reason, this ceramic material cannot be used in multilayer capacitors with electrodes of base metal materials. This is because the sintering temperature is higher than the melting point of the electrode material and the electrode material is oxidized because it is sintered in air. In contrast, when ceramic materials are sintered at low temperatures, pores remain in the dielectric, resulting in poor electrical properties, and these materials cannot be sintered in an atmosphere with a low oxygen partial pressure. When connected, the electrical properties deteriorate further and particularly high dielectric losses occur at frequencies below 10 ⁵ Hz. Generally, sintering is used to reduce the porosity of green sintered ceramic materials and is ineffective if the temperature is too low. The object of the present invention is to provide a ceramic dielectric with good electrical and dielectric properties that can be sintered, and for this purpose base metals such as nickel (Ni) or cobalt (Co) are used as electrode material. be able to. The present invention uses iron group metals or manganese as doping agents in the form of carbonates or oxides.
(Zr _1-x Ti _x )O ₃ (where E represents an alkaline earth metal ion and satisfies the requirement of 0<x0.07)
This is achieved by adding a stoichiometric perovskite starting mixture of the composition: and sintering the assembly in a reducing atmosphere to obtain a dense structure. In a preferred embodiment of the present invention, 0.2 to 1.2 mol% of iron (Fe) or nickel (Ni) is used as the iron group metal.
Also, manganese (Mn) is added in a proportion of 0.1 to 1.2 mol%. In this case, metals of the iron group or manganese are added as dopants to the perovskite compound, so that the amounts of these additives indicate the amounts as dopants to the perovskite compound. In particular, advantageous capacitor properties are achieved by a preferred embodiment of the present invention in a perovskite compound defined by the composition CaZr _0.985 Ti _0.015 O ₃ with 0.5-1.0 mol% manganese (Mn).
or when adding 1.0 mol% iron (Fe), 0.2 to 1.0 mol% manganese (Mn) or 0.5 to 1.0 mol% iron (Fe) or 0.5 mol to the perovskite compound defined by the composition SrZr _0.955 Ti _0.045 O ₃ Obtained when adding % nickel (Ni). The sintering operation is carried out after mixing the compound forming the perovskite phase with the compound of the metal to be added.
A temperature range of 1200° C. is advantageous since the CO ₂ is already separated from the carbonate. If no gas is generated during the subsequent sintering step, the final product will have a dense structure. Firing has the added advantage of starting the formation of the perovskite structure as early as in the firing operation. The advantages obtained by the method of the invention are that it is possible to produce ceramic dielectrics with optimum ceramic, electrical and dielectric properties at particularly low sintering temperatures, and that in the sintering atmosphere base metals, i.e. inexpensive The metal can be used as an electrode material instead of the noble metals palladium and platinum. The ceramic material produced is a single phase and homogeneous material. The following table shows the composition of one example perovskite compound and indicates the abbreviations used for these compounds.

[Table] Next, the present invention will be described with reference to the accompanying drawings. Figure 1 shows the change in insulation resistance ρ of SZT with 0.5 mol% manganese added. For example, the value of the insulation resistance at temperatures below 150 ° C, sintered in a mixed gas MG (flow of a mixture of humidified N ₂ and 25% H ₂ ) is ≫ 10 ¹² ohms; capacitors with such dielectrics are suitable It has excellent insulation operation. Figure 2 shows the change in loss angle tan δ at ambient temperature in the range of 1 MHz to 50 MHz measured for SZT doped with 0.5 mol% manganese. Values below 10 ^-4 are loss angles tantan δ obtained for samples sintered in a mixed gas atmosphere. The samples were sintered at 1450℃ and 1400℃. Figure 3 shows the 10k
It shows the variation of loss angle δ and dielectric constant ε in Hz. The temperature coefficient of permittivity TC〓 can be expressed by the following formula, and this temperature coefficient was obtained for ε: TC〓=ε−ε ₂₅ /ε ₂₅ ×0 ⁶ =8×10 ^-6 /℃ This The dielectric loss of ceramic materials is kept below 10 ^-3 at temperatures up to 150°C. The sample is
Sintered at temperatures of 1450℃ and 1400℃. FIG. 4 shows a partially cutaway perspective view of a ceramic multilayer capacitor. The dielectric for the multilayer capacitor shown in FIG. 4 is formed in the form of a thin ceramic film 11 having a thickness in the range from 15 to 100 μm and having a sandwich structure with electrodes 21, 22;
The individual electrode layers are electrically connected via terminals 2,
One terminal is connected to each of the electrode layers 21 and 22. In this connection means, the electrode layers 21 and 22 are stacked one on top of the other, and for this purpose one layer of the alternating stack is extended to two opposite outer areas of the sandwich structure formed from the ceramic film of the dielectric 1 and the electrode layers 21, 22. make it exist The ceramic dielectric 1 for the multilayer capacitor shown in FIG. Alternatively, an electrode material having a lower melting point and higher oxidizability than platinum can be used. For example, the electrode layer 2 may be made of nickel or cobalt, which are significantly cheaper than the noble metals palladium or platinum.
1 and 22. The composition of the ceramic material for the dielectric is Ca
(Zr _1-x Ti _x )O ₃ and Sr(Zr _1-x Ti _x )O ₃ (where x is
(indicating values up to 0.07). Manganese in the form of carbonate MnCO ₃ as well as
Iron and nickel in oxide form are particularly suitable as additives to perovskite starting materials. Extremely pure quality rutile TiO ₂ , ZrO ₂ ,
BaCO ₃ , SrCO ₃ and CaCO ₃ can be used as starting materials for perovskite compounds. All compounds used as additives should be extremely pure. When making test specimens of ceramic samples for measurement purposes, all starting materials, i.e. those for the perovskite compound and for the relevant additives, are weighed and mixed to match the desired composition, and then added to the planetary form. Suspended in alcohol on a ball mill for 2 hours. The powder is dried and then pre-sintered in air at 1200°C for 15 hours, after which the powder thus sintered is ground in a planetary ball mill for 1 hour to give a
A 7×7×20 mm ³ rod with a density of 65% was pressurized mechanically and hydraulically. humidify rod
Sintered in a mixed stream of N ₂ and 25% H ₂ (this gas mixture is hereinafter referred to as mixed gas MG). Humidification of the gas requires a H ₂ / ^H ₂ O ratio of 7.7 (i.e.
The amount of H ₂ is 7.7 times the amount of H ₂ O).
The samples were heated and cooled at a rate of approximately 3° C./min, and the samples were maintained at maximum temperature, ie, the sintering temperature shown in the table, for 15 hours. This sintering temperature varies depending on the sample. To measure the electrical and dielectric properties shown in Figures 1-3 of ceramic materials, samples were
It was made in the form of a sintered rod formed into a cylindrical disk with a thickness of 0.15 mm and a thickness of 0.15 mm. 5mm thick chrome
A nickel (CrNi) layer and a 150 mm thick gold layer were deposited on opposite sides of these discs. in this case,
The gold layer is deposited on the CrNi layer to protect against corrosion.
and improve electrical contact. Although the loss angle tan δ and the dielectric constant ε depend on temperature and frequency, the capacitance and dielectric constant of the sample were measured in the range of 100 Hz to 50 MHz. The dependence of ε and tan δ on the amplitude of the alternating electric field in the range 100-10000 V/cm was measured at 10 kHz at ambient temperature. The resistivity of the ceramic material was determined at each temperature by measuring the leakage current at 70 seconds after applying a constant electric field strength of 1 V/μm. Samples of stoichiometric composition with the doping material shown in the table sintered to sufficient density and with appropriate microstructure were heated at 1400 °C and 1450 °C in a humidified _N2 atmosphere containing 25% _H2 . Prepared at a sintering temperature of °C.

[Table] The following table shows the sintering conditions, dielectric properties, and electrical properties of the samples prepared as described above.

【table】

Table: In the table, T _s indicates the minimum sintering temperature at which the ceramic material has a density of at least 95%, and TC indicates the average temperature coefficient of ε in the range 25-125°C. In the TC column, values enclosed in brackets indicate that the temperature coefficient changed significantly in a nonlinear manner with a high temperature coefficient. A dielectric of perovskite compound stoichiometric composition Sr _0.955 Ti _0.045 O ₃ doped with 0.5 mol % manganese is extremely advantageous for the production of multilayer capacitors. Densities above 95% were obtained at sintering temperatures of 1400°C and 1450°C. Figures 1, 2 and 3 show the temperature dependence of the insulation resistance, ε and tan δ as a function of temperature, and the dependence of tan δ on frequency for this type of dielectric. Investigation of the dependence of the dielectric constant ε and the dependence of the loss angle tan δ on the amplitude of the alternating electric field showed no appreciable changes in ε and tan δ for this ceramic material up to at least 10 kV/cm. The results of life tests measuring insulation resistance and density values for this type of ceramic material are shown in the following table and.

Table V shows the density as a percentage of the theoretical density for ceramic materials of the above type at two different sintering temperatures and different sintering atmospheres.

[Table] The following process was applied to the production of a multilayer capacitor having a dielectric of stoichiometric composition SrZr _0.955 Ti _0.045 O ₃ and doped with 0.5 mol % manganese. Composition SrZr _0.955
A ground ceramic mixture with Ti _0.045 O ₃ +0.5 mol % MnO ₂ was prepared by first pre-sintering at 1200°C.
This powder was suspended in 30% by weight deionized water with a wetting agent. This suspension was intimately mixed in a dispersion mill with an organic binder, such as a polymerized hydrocarbon, and a plasticizer. As the plasticizer, for example, triethylene glycol can be used. The suspension thus obtained was degassed under voltage and stirred with a wetting agent.
A thin layer of this suspension was drawn from the overflow vessel by a rotating steel belt and dried into a ceramic film approximately 40 μm thick. The number of unfired ceramic film sections required for the desired capacitor thickness was then stacked. An electrode layer approximately 9 μm thick was provided between these films. These electrode layers consist of nickel powder with a particle size of approximately 0.2-0.8 μm and an organic binder such as cellulose acetate. Thereafter, the stack was pressed and punched to form a monolithic multilayer block. The blocks were heated at 600 DEG C. at a rate of 0.5 DEG C./min in an _N2 / _O2 atmosphere with a volume ratio of 5:1 to 100:1 to evaporate the solvent and burn out the binder. After that, the block is heated to 1400 in a reducing atmosphere.
℃ at a rate of 3° C./min and sintered at this temperature for 10 hours. The reducing atmosphere consisted of _N2 and _H2 in a 1:4 volume ratio, with the _H2O- content adjusted by humidifying the gas mixture at 25 °C (i.e., _H2O -containing The amount was maintained at the desired level by passing the gas mixture through water at a temperature of 25°C). After sintering, the block was cooled to room temperature at a rate of 3° C./min without changing the atmosphere. The sintered monolithic block was provided with electrical terminals which could be suitably deposited and soldered by baking a mixture of nickel and glass powder in the atmosphere described above. The electrical characteristics of three different samples of these multilayer capacitors are shown in the following table:

【table】

[Table] Capacitance and loss angle δ are frequency =
Measurements were made at 10kHz and AC electric field amplitude E=20kV/cm. Also, known processes other than those mentioned above, such as prettifying, spraying or doctor-blading, can be used to create the film portions. Also, CO/
Other reducing gas mixtures such as _CO2 , Ar/ _H2 , etc. can be used in place of the above reducing atmosphere consisting of a humidified _N2 / _H2 mixture. Also, instead of nickel powder, other base metals such as iron, cobalt or alloys of two or three metals can be used for the electrode layer.

[Brief explanation of the drawing]

Figure 1 is a curve diagram showing the change in insulation resistance of SZT added with 0.5 mol% manganese, and Figure 2 is a curve diagram showing the change in insulation resistance of SZT added with 0.5 mol% manganese.
A curve diagram showing the change in loss angle tan δ at ambient temperature in the range from Hz to 50 MHz. Figure 3 shows the dielectric constant ε and loss at 10 kHz in the ambient temperature range of 150°C measured for SZT with 0.5 mol% manganese added. A curve diagram showing changes in the angle tan δ, and FIG. 4 are a partially cutaway perspective view of a ceramic multilayer capacitor. 1... Ceramic dielectric, 2... Terminal, 11...
... Ceramic film, 21, 22 ... Electrode (electrode layer).

Claims (1)

[Claims] 1. A method for producing a dielectric material having a perovskite structure starting from alkaline earth zirconates in which zirconium is partially substituted with titanium, in which a metal is used as a doping agent in the form of a carbonate or an oxide. , E(Zr _1-x Ti _x )O ₃ (where E represents an alkaline earth metal ion, and 0<x0.07
iron as the metal for the doping agent in this case 0.2 to 1.2
mol%, nickel in a proportion of 0.2-1.2 mol% and manganese in a proportion of 0.1-1.2 mol%, and the assemblage is sintered in a reducing atmosphere to obtain a dense structure. Method of manufacturing dielectric material. 2. The method according to claim 1, wherein manganese is added to a perovskite compound having the composition CaZr _0.985 Ti _0.015 O ₃ in an amount of 0.2 to 1.2 mol % based on the compound. 3. The method according to claim 1, wherein iron is added to a perovskite compound having the composition CaZr _0.985 Ti _0.015 O ₃ in an amount of 0.5 to 1.2 mol % based on the compound. 4. The method according to claim 1, wherein manganese is added to a perovskite compound having the composition SrZr _0.955 Ti _0.045 O ₃ in an amount of 0.1 to 1.2 mol % based on the compound. 5. The method according to claim 1, wherein 0.2 to 1.2 mol % of iron is added to a perovskite compound having the composition SrZr _0.955 Ti _0.045 O ₃ based on the compound. 6. The method according to claim 1, wherein nickel is added to a perovskite compound having the composition SrZr _0.955 Ti _0.045 O ₃ in an amount of 0.2 to 1.0 mol % based on the compound. 7. After mixing the compound forming the perovskite phase with the metal compound to be added, sintering is carried out at 1100 °C.
carried out at a temperature range of ~1200 °C, after which the product is ground, shaped and then heated to 1320 °C in a reducing atmosphere.
2. A method according to claim 1, wherein the method is sintered at a temperature in the range of -1450<0>C.